How a Whale Senses the World

Whales
and dolphins (known in the scientific world as Cetaceans), have
undergone incredible changes to their sensory systems in order to
adapt to life in the sea. Ancestors of these remarkable creatures
were actually land animals that looked something like this animal to
the right. Over many millions of years they began to lose certain
abilities that were necessary for land dwelling and replaced them
with very unique abilities suited for an aquatic life.

One of the first ancestors of whales and dolphins

The eye of a whale

The eye of a humpback whale

A beluga whale blowing bubble rings

A humpback whale coming up to breathe

A bottlenose dolphin

Two killer whales

A killer whale

A dolphin and calf

Spotted dolphins

An amazon river dolphin

Northern Right Whale

Vision

Being
able to see underwater requires a special lens shape. Light travels
more slowly in water than it does in the air. It also refracts or
bends when it passes into the water. So ancient cetaceans originally
possessed eyes suited for living on land and were at a disadvantage
when trying to hunt fish. As a result they were able to develop an
eye that is suited to both air and sea. They did this by evolving to
have strong muscles around the eye that can actually change the shape
of the lens depending on whether it is exposed to air or water.

There
is another problem that was faced by the eyes of ancient cetaceans.
The intensity of light at the surface is much higher than it is at
lower depths or in murky water. A whale needs to be able to see in
both situations. Sperm whales, for example, spend much of their time
at great depths where there little or no light can reach. As a
result, cetaceans have evolved to have a very large pupil that can
open wide to allow a large amount of light in at great depths. They
also have what is known as a tapetum lucidum, which is a light
reflecting layer that sends light back through the retina a second
time, creating a higher quality image. When they rise to the
surface, they simply close their pupil to a tiny slit, only allowing
a small amount of the light in.

Whales
and dolphins usually turn on their sides to focus one eye on a
target, however they are capable of binocular vision for a small
distance. While underwater, they can usually see about 35 feet in
front of them. Above the surface however, they become more
nearsighted as a result of the change in pressure and air density.

Smell

Whales
and dolphins have all but lost their sense of smell. This could be a
result of evolution. It is reasonable to assume that as the
repositioning of the nostrils to the top of the head was occurring,
many changes to the function of the organs associated with the
nostrils must have also occurred. Baleen whales have a limited sense
of smell, perhaps to help them locate krill or plankton which have
distinct smells that can be picked up in the air as the whale takes a
breath. Toothed whales appear to have completely lost their
olfactory system.

Taste

Cetaceans
do seem to have the ability to taste. Dolphins have shown the
ability to detect sweet, sour, bitter and salty flavors. It is also
quite common for whales and dolphins to refuse dead fish, or prefer
one type of fish over another. Some even have a small Jacobson's
organ which you may know is also found in cats and snakes among
others.

Hearing

Sound
travels five times as fast underwater as it does in the air. The
difference in density between the air and the sea makes it difficult
for sound to pass between them. As a result, a normal air-filled
mammal ear is useless. Baleen whales and toothed whales have evolved
different ways of dealing with this problem and it is not completely
understood in both types. Baleen whales have a waxy plug in their
ear canal which is thought to transmit sounds to the inner ear. This
means they are most likely deaf above the water. Toothed whales do
not have this ear plug. There are several theories for how these
whales hear but in my opinion the most logical theory is that the ear
canal is closed off in most toothed whales and has become redundant.
Instead, toothed whales may be able to receive sounds through their
lower jaw which contains oil-filled sinuses that may be able to
transmit sounds directly to the inner ear. Or perhaps they can hear
some sounds through a water filled ear canal and use their lower jaw
only for picking up echolocation clicks.

Echolocation

Although
I plan to dedicate a separate hub to this fascinating ability, I
thought it would be appropriate to summarize what this sense is and
what it does for those who have never heard of it.

Echolocation
involves emitting sounds in the form of short clicks and picking up
information about the world surrounding the dolphin by analysis of
the returning echoes. This ability is only found in toothed whales, dolphins, as well as bats and possibly some bird species. They combine low and high frequency sound emissions
along with exceptional directional hearing which has given them an
edge over other sea animals.

Touch

Cetaceans
may not have hands but their sense of touch is still very important
to them. Their skin is soft and easily damaged but it also heals
quite quickly. It is highly specialized and contains a complex
system of nerve endings which are more abundant in certain areas. It
is believed that cetaceans can use their sense of touch to achieve
“laminar flow” of water over their bodies to swim efficiently at
high speeds. If turbulence develops somewhere on the surface of the
skin, the pressure should help the dolphin adjust its body to keep
the correct shape for laminar flow to occur. These creatures also
need their sense of touch to know when their blowhole is above the
surface of the water, allowing them to take a breath. They have many
more nerve endings around the blowhole to help with this. In
addition they possess sensitive nerve endings on the tips of their
mouths to help investigate objects, much like our fingertips.

The Magnetic Sense

Of
all the senses described here, this is the least understood. Small
crystals of magnetite have been found in many species including
bacteria, bees, butterflies, fish, birds, bats and reptiles. They
have also been found in and around the brains of Cetaceans.
Magnetite crystals are thought to continuously orient themselves to
the earth's magnetic field, like miniature magnets. Perhaps these
animals are able to sense the orientation of these crystals and work
out the direction in which it is traveling. Normally the magnetic
fields run north to south at an even density. Occasionally however,
it will be distorted by certain geographical formations that are rich
in metals like iron. These formations are called geomagnetic
anomalies. It is possible that this is one of the causes of
strandings by whales and dolphins.

In
conclusion, cetaceans have adapted to live in a completely alien
world compared to ours. Although we are both air breathing mammals,
whales and dolphins have been evolving for so long (around 54 million
years) that they have become extraordinarily unique animals.